1. Field of the Invention
The present invention relates to a liquid crystal display device and a method for repairing a breakage of circuit lines thereof and, particularly, a method for repairing a breakage of at least one of circuit lines formed on a thin film transistor (TFT) substrate of an active matrix type liquid crystal display panel.
2. Description of the Prior Art
Japanese Patent Application laid-open No. H5-5896 discloses an example of a conventional circuit line breakage repairing method for repairing a broken circuit line formed on a TFT substrate. The repairing method disclosed therein will be described with reference to FIGS. 1 and 2 in which FIG. 1 is a plan view of a pixel portion constituting an active matrix type liquid crystal display and FIG. 2 shows a broken portion 14 of a circuit line shown in FIG. 1 in an enlarged scale for explaining the repairing method therefor.
In FIG. 1, each signal line 3 as the circuit line, which strides over a plurality of scan lines 2, has a pair of wider portions 301 on both sides of each scan line 2 and end portions of the wider portions 301 are overlapped on one end portions of first electrically conductive members 30 through insulating films, respectively. The other end portions of the first electrically conductive members 30 are overlapped on opposite end portions of a second electrically conductive member 40, which strides across the scan line 2, through insulating films, respectively.
In a case where the signal line 3 is broken at a portion indicated by 14, the overlapping portions (31 and 32 in FIG. 2) of the first electrically conductive member 30 and the second electrically conductive member 40 and the overlapping portions (33 and 34 in FIG. 2) of the signal line 3 and the first electrically conductive member 30 are irradiated with laser light to melt the insulating films between them to thereby electrically connect the electrically conductive members to thereby form a bypass line for the broken portion 14 of the signal line 3, as shown in FIG. 2.
However, since the signal line 3 has to have the wider portions 301, there are a problem of reduction of aperture ratio of a pixel and a problem of impossibility of repair of a breakage of the circuit line when the latter is a scan line since a correction pattern such as mentioned above is not provided in the scan line.
A method for solving such problems disclosed in Japanese Patent Application Laid-open No. H9-146121 will be described with reference to FIG. 3, which is a plan view of a liquid crystal display disclosed therein.
In FIG. 3, the liquid crystal display panel is constructed with a transparent substrate 1 of an insulating material, a plurality of scan lines 2, which are arranged horizontally in parallel to each other with a constant gap formed on the transparent insulating substrate 1, a plurality of signal lines 3, which are arranged vertically in parallel to each other with a constant gap, formed on the transparent substrate 1, an insulating film electrically separating the scan lines 2 from the signal lines 3, a thin film transistor (TFT) 5 provided in each of cross portions of the scan lines 2 and the signal lines 3, a plurality of terminal 7 connected to one end portions of the scan lines 2 and the signal lines 3 and a plurality of auxiliary wiring 49 provided to surround a peripheral portion of a display region in which the thin film transistors 5 are arranged.
When a breakage occurs in one of the scan lines or the signal lines, the broken line is connected to the auxiliary wiring by irradiating the cross portion between the broken line and the auxiliary wiring 49. That is the auxiliary wiring is used as a bypass line for a broken portion of the scan or signal line.
In this technique, however, the auxiliary wiring is in a floating state electrically. Therefore, there is a problem that, in a case where electric charge is accumulated on the auxiliary wiring, electrostatic breakdown tends to occur since the electric charge can not be dispersed. Furthermore, there is another problem that, since a plurality of auxiliary wiring are provided, a space between an outer periphery of the display portion and an outer periphery of a substrate opposing to the transparent substrate, that is, a frame size, is increased.
Japanese Patent Application Laid-open No. H8-171081 discloses, as means for preventing electrostatic breakdown of the liquid crystal display panel, a construction in which a buffer portion is provided in an auxiliary wiring.
In the construction disclosed in Japanese Patent Application Laid-open No. H8-171081, however, since the auxiliary wiring extend on not only a TFT substrate but also a drive circuit substrate connected externally of the liquid crystal panel, a repair of a broken line has to be performed after a step (module step) for connecting the drive circuit substrate to the TFT substrate. Since it is practical that the breakdown of line tends to occur in a step (panel step) for forming the TFT substrate, it is preferable that the repair is performed prior to the module step, if possible.
Further, in the construction disclosed in Japanese Patent Application Laid-open No. H8-171081, there is a problem that the electrostatic breakdown occurs in assembling a polarizer plate in the panel step since the auxiliary wiring is in an electrically floating state during the panel step.
An object of the present invention is to provide a liquid crystal display device equipped with an inexpensive construction for repairing breakdown of circuit lines thereof and a method for repairing a breakdown of circuit lines of the liquid crystal display device.
Another object of the present invention is to provide a construction of a liquid crystal display device in which, when a circuit line breakdown occurs in a scan line or a signal line thereof, the broken portion of the circuit line can be easily and reliably repaired and a method for repairing the liquid crystal display device.
In order to achieve the above objects, according to the first aspect of the present invention, a liquid crystal display device in which an auxiliary wiring and one of circuit lines, which has a broken portion, are short-circuited at cross points thereof by irradiating the cross points by laser light such that the auxiliary wiring is used as a bypass circuit, is featured by that an electrostatic protective element is provided in each cross portion of the auxiliary wiring and the circuit lines and the auxiliary wiring is selectively separated from a common terminal to which a potential is applied from a signal processing substrate of the liquid crystal display device.
According to the second aspect of the present invention, a wiring breakage repairing method for repairing a broken circuit line in a liquid crystal display device including an auxiliary wiring, which crosses opposite end portions of scan lines and signal lines and is applied with a constant potential, and electrostatic protective elements each provided in each cross portion, is featured by comprising the steps of irradiating a cross portion of the auxiliary wiring and a scan line or a signal line, which has a broken portion, with laser light, cutting away a connecting pattern between a common terminal and the auxiliary wiring or separating a signal processing substrate for applying a potential to the auxiliary wiring from the auxiliary wiring and using the auxiliary wiring as a bypass line for the broken line.
In a liquid crystal display device constructed such that cross points between an auxiliary wiring and one of circuit lines, which has a broken portion, are short-circuited to use the auxiliary wiring as a bypass line for the broken portion, the present invention is featured by that an electrostatic protective element is provided in each of the cross points between the auxiliary wiring and the circuit lines and the auxiliary wiring can be switched off from a state in which the auxiliary wiring is fixed to a certain constant potential applied from a drive circuit substrate to an opposing substrate through a common terminal (COM terminal).
Particularly, the liquid crystal display device is featured by that it includes a thin film transistor substrate of the active matrix type, that the circuit lines constitute the signal lines and the scan lines, which are orthogonal to and electrically separated from the signal lines by an insulating film, are connected to the respective thin film transistors, that a first region portion of the auxiliary wiring, which is in parallel to the signal lines, are formed in a plane coplanar with a plane in which the signal lines are formed, that a second region portion of the auxiliary wiring, which is in parallel to the scan lines, are formed on in a plane coplanar with a plane in which the scan lines are formed and that the first region portion and the second region portion of the auxiliary wiring are electrically connected each other through through-holes formed in the insulating film.
Furthermore, the liquid crystal display device is featured by that the liquid crystal display device includes a drive circuit substrate electrically connected to a thin film transistor substrate, that the auxiliary wiring formed on the thin film transistor substrate is electrically connected to the COM terminal provided on the drive circuit substrate and that supply cut-off means such as a zero ohm resister is detachably provided on the drive circuit substrate.
Alternatively, the liquid crystal display device is featured by that it includes a drive circuit substrate electrically connected to the thin film transistor substrate, that a plurality of supply terminals provided on the drive circuit substrate and kept at a common potential and terminals of the auxiliary wiring provided on the thin film transistor substrate are electrically connected each other and that a cut pattern having a narrowed portion is provided between the auxiliary wiring terminals and the auxiliary wiring.
Moreover, according to the present invention, a broken line repair method for repairing a defective circuit line having a broken portion by electrically connecting an auxiliary wiring to a circuit line, which has a breakage, of a liquid crystal display device by irradiating cross points of the auxiliary wiring and the defective circuit line to remove the insulating film therebetween to thereby use the auxiliary wiring as a bypass line for the broken portion of the defective circuit line is featured by comprising the steps of electrically connecting the auxiliary wiring to the defective circuit line while the auxiliary wiring is fixed to a constant potential applied to an opposing substrate through the terminals (COM terminals) to which a certain constant potential is applied from the drive circuit substrate and, then, of cutting off the application of the constant potential to the auxiliary wiring.
The electrically connecting step is performed in a state where the electrostatic protective elements are provided in the cross points between the auxiliary wiring and the circuit wiring.
Furthermore, the cutting step is performed by removing the short-circuit member such as chip type zero ohm resistor provided on the signal processing substrate.
Alternatively, the cutting step is performed by cutting the narrowed portion of the cut pattern provided between the common potential supply terminals, that is, the COM terminals, and the auxiliary wiring.